Frozen, partially fried root vegetable products that only require a short period of further cooking before serving are widely available and used in both the food service markets and consumer markets. Such products are generally referred to as par fried products. Par fried root vegetable products are typically made from root vegetables such as potatoes, yams, carrots, beets, yucca and sweet potato. The most common par fried root vegetable products are made from potatoes (par fried potato products). Due to the large market for par fried products, there is a constant demand for better products and improved methods for producing such products.
One desired improvement is the reduction of reconstitution (ie. final cooking) time from the par fried product to the finished product to be eaten by the consumer. The fastest method for reconstitution is by frying. However, there is still a desire to reduce this finish frying time further to improve process efficiencies while maintaining, or improving, final product characteristics.
The purpose of the finish fry step is to cook the par fried product, for example, by browning the product and removing moisture from the par fried product to an extent that the par fried product acquires the texture and other properties of the cooked product. A par fried product having a higher moisture content entering into the finish frying step, will require a longer finish frying time to remove moisture and produce a consumable product with desired properties.
A number of solutions have been proposed to reduce the moisture content of the final par fried product and thus reduce the finish frying time.
In general, prior methods for reducing the moisture content of par fried potato products focused on the use of the frying process. Frying provides an even and consistent method of heat transfer because the oil is in full contact with the entire surface area of the immersed potato pieces. Furthermore, the frying process permits a very fast rate of heat transfer to the potato pieces. Frying is considered desirable in a plant setting to ensure a rapid production rate.
For example, one method for further reducing the moisture content of par fried potato products is by extending the par frying time. However, for potato products, excessive par frying causes loss of volatiles leading to degradation of potato flavour. It also caramelizes the sugar on the potato surface which causes colour change, and creates mottling and variation, which are coloured spots or blotches of colour caused by the scorching of the potato surface from the hot frying temperatures.
Another example of a method for further reducing the moisture content of par fried potato products is a two-step par fry method which reduces the moisture content of the potato product in two discrete frying steps such as in U.S. Pat. No. 5,753,291 to Pederson et al. Typically, the two-step par fry method allows greater moisture removal than is achievable in a conventional single par fry step of the same overall frying time. However, the two-step par fry method does not avoid all of the negative effects of extended par frying. Further, a two-step par fry method is inefficient because it reduces the line rate in the factory (i.e. the rate of production of product), requires more equipment and the use of more oil for heating. The inefficiencies of the process increase the effort and time required to produce the products. As well, a third frying step subjects the product to additional heat necessary to finish fry (cook) the product.
A further example of a method for reducing the moisture content of par fried potato products is a two-step par fry process with an intermediate freezing step (fry-freeze-fry) as disclosed for example in U.S. Pat. No. 4,590,080 to Pinegar and U.S. Pat. No. 6,548,093 to Collinge et al. The fry-freeze-fry process is another example of a process that attempts to reduce the negative effects of extended par frying. The fry-freeze-fry process has the advantages of increased moisture removal of a two-step par fry process. It also reduces the negative effects of the second par fry by freezing the product after the first par fry. When the frozen product enters the second par fry, a substantial initial portion of the second par fry step is required to thaw and reheat the frozen product back to frying temperature whereby the product is actually maintained at frying temperature for a substantially shorter time period. The reduced time that the product is subjected to frying temperatures reduces the negative effects of frying. However, a fry-freeze-fry process has similar inefficiency problems as the two-step process described above. The fry-freeze-fry process also produces potato products that tend to lack flavour and have more variability in texture and quality.
Equilibration is another technique used for reducing the negative effects of frying. The equilibration step is typically used after an initial drying step that involves applying heat to the product to dry it. This initial drying step precedes par frying. The equilibration step is a resting step where the moisture from the center of the cooling product is allowed to rehydrate the surface of the product. The surface is typically drier from being closer to the heating source. The negative effects of extended par frying are reduced when the product has been equilibrated in this manner prior to par frying. Equilibration decreases the moisture difference between the surface and the center of the product which reduces case hardening or effects of excessive drying. The equilibration step typically involves resting the product on a conveyor for 1-5 minutes at ambient temperature or circulating unheated air over the product for 1-5 minutes. Equilibration would usually provide less than 0.5% weight loss/minute, and this rate would decrease as the product cooled. Equilibration has also been used between two frying steps (fry-equilibrate-fry process) to produce high solids French fries, typically in excess of 45% solids. Conventional French fries have solids of less than 36% so in a process to produce high solids French fries, the second fry would typically increase solids from less than 36% to 45% or higher.
There is a need for an improved method for producing par fried products that have a more rapid reconstitution time and maintain or improve upon the quality, texture and appearance of a conventional reconstituted product.